We can find the increase in operating income for each $ 1,000 increase in revenue per month by finding the contribution margin ratio and the multiplying it with the increase operating income of $ 1,000 each.
The formula to find the contribution margin ratio is :-
Contribution margin ratio = Contribution margin per unit / Selling price per unit
= 12 / 20 = 60%
The increase in operating income = Contribution margin ratio * Revenue
= 60 % * 1,000
= $ 600
The calculations are shown below :-
Selling price per unit = $ 20
Variable cost per unit = $ 8
Contribution margin per unit = Selling price per unit - Variable cost per unit
= $ 20 - $ 8 = $ 12
